As is known in the art, an optical fiber is a slender bar-like optical light-transmitting element comprising a core and a sheathing layer concentric therewith which is made of a material having a lower refractive index than said core. Such optical fiber functions optically as a light-transmitting element to transmit light incident on one end thereof to the other end through the core while allowing the light to totally reflect on the interface between the core and the sheathing layer. In recent years, optical fibers of this type have been in great demand for use as light-transmitting elements for optical illumination devices including optical systems. Conventionally, optical illumination devices using this type of optical fibers have a disadvantage that it is very difficult to arrange and support the illuminating end side of a number of optical fibers in such a manner as to respresent a desired pattern, such as a letter or figure.